In the field of graphic arts, an image-formation system providing a super-high contrast photographic characteristic, especially a gamma of 10 or more, is required for satisfactory reproduction of continuous tone images or line images by dot images. For this purpose, a specific developer called a lith developer is generally used. The lith developer contains, as a developing agent, hydroquinone and, as a preservative, a sulfite in the form of an adduct with formaldehyde so as to control the free sulfite ion at an extremely low level, usually not more than 0.1 mol/l, thereby preventing deterioration of the infectious development ability of the developing agent. The lith developer has a serious disadvantage in that it is very susceptible to air oxidation and cannot withstand use for a long period of time exceeding 3 days.
Known processes for obtaining high contrast photographic characteristics with a stable developer include the process of using hydrazine derivatives as described in U.S. Pat. Nos. 4,224,401, 4,168,977, 4,166,742, 4,311,781, 4,272,606, 4,211,857 and 4,243,739, etc. This process provides super-high contrast and high sensitivity, and also ensures greatly improved stability of the developer against air oxidation as compared to the conventional lith developer because of the high permissible sulfite ion concentration in the developer.
However, it has been found that the image formation system employing the hydrazine derivatives tends to cause black spots called black pepper on non-image area, for example, between dots. This phenomenon becomes particularly conspicuous when the sulfite ion content in a developer is decreased or the pH of a developer increases due to fatigue of the developer, and causes significant impairment of photographic quality.
Various attempts have hitherto been made in order to eliminate the problem of black spots, but ad hoc improvement frequently accompanies reduction in sensitivity and gamma. In particular, no means has been proposed for solving the problem of black spots without hindering the effect of the above-described hydrazine compounds to increase sensitivity and contrast.